This invention relates generally to the field of electronic control systems for automotive engines and more particularly to power supplies for microprocessor-based engine fuel control systems.
In this day of rising fuel costs, the conservation of energy through the use of electronically controlled engines and fuel systems has become increasingly important. One major problem in equipping an automotive vehicle with a suitable electronic control system is that under cold cranking conditions, the battery supplying electrical power to the vehicle may have its output voltage drop to as low as four volts and still start the engine. Since microprocessor-based engine control systems typically require a tightly regulated five volt supply capable of delivering hundreds of milliamps, conventional series linear regulators or series switching regulators are incapable of delivering the necessary output when the battery output is at four volts, since neither type of regulator can boost voltage.
For a vehicle equipped with microprocessor-based engine control systems, the problem presented by low battery voltage during cold cranking could be solved in several ways. First, the vehicle could be equipped with a larger than otherwise necessary battery and charging system to prevent the battery voltage from dropping below acceptable levels when the vehicle is started. Second, the electronic engine control system could be equipped with sufficient intelligence at the input/output points of the system to start the engine without utilizing the intelligence of the microprocessor. Third, the vehicle could be equipped with an electronic power supply capable of boosting battery voltage as required to handle low battery voltage conditions encountered during cold cranking.
In addition to being expensive, the first option above involves a significant weight penalty which partially defeats the purpose for using microprocessor-based engine control systems, that is the conservation of fuel. The second option may be a suitable choice for control systems not involving the sophisticated regulation of fuel during start-up under cold cranking conditions. It is felt, however, that microprocessor control of fuel delivery during start-up conditions is desirable, if not essential, to provide the control flexibility needed to be able to quickly adapt to future advances in fuel control technology, including those in individual cylinder fuel injection systems and throttle body injection systems. Thus, controlling fuel delivery during engine start-up by providing intelligent input-output circuitry is believed to be unduly burdensome, not only due to the sophistication which would be required, but also due to the inherent inflexibility of such circuitry.
The third option, then, is deemed to be preferred with microprocessor-based engine control systems which include fuel control because it provides full microprocessor capability to control fuel delivery during engine start-up, and also because it is believed to represent in many cases the least expensive option since intelligent input-output circuitry is not needed.
Accordingly, it is an object of the present invention to provide an electronic power supply for regulating electrical power available from an automotive battery to produce a suitable DC output voltage and current for operating an electronic engine control system.
Another object of the present invention is to provide a power supply for providing suitable voltage and current to operate a microprocessor-based engine control system during cold cranking conditions when the output voltage of the vehicle's battery drops as low as four volts.
Yet another object of the present invention is to provide a power supply which has minimal power dissipation so as to optimize reliability, and to allow location of the power supply circuitry in close proximity to the other electronics in a microprocessor-based engine control system.
One more object of the present invention is to provide a power supply having a shunt switching regulator section which provides a variable voltage boost function as needed to compensate for the variable low battery voltages encountered during engine start-ups.
An additional object of the present invention is to provide a power supply which is relatively inexpensive and simple to fabricate.
Still another object is to provide a power supply having a series switching regulator section provided with a two-winding transformer, and a shunt switching regulator section, wherein the two sections share the same transformer thereby minimizing cost.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.
The present invention achieves the foregoing objects by providing a power supply having a series switching regulator section provided with a two-winding transformer, and a shunt switching regulator section that shares the transformer with the series switching regulator section. The series regulator section, by utilizing the transformer, steps down the supply voltage when necessary to produce the desired DC output voltage, while the shunt regulator section, by utilizing the transformer, steps up or boosts the supply voltage when necessary to produce the desired DC output voltage. The use of a switching regulator design for both sections of the power supply provides the required output voltage and current without the unnecessary power dissipation found in linear regulator designs.
The supply voltage boost provided by the shunt regulator section of the power supply is proportional to the drop in battery voltage from its nominal value when the vehicle is running. In this manner, the variable boost provided smoothly compensates for any reduced battery voltages encountered during engine operation, whether they be the greatly reduced battery voltages encountered during cold cranking conditions, or the slight reductions provided by a battery not being properly charged by the alternator system of the vehicle due to such conditions as a loose fan belt and the like.